Isotopes and Impact: A Cautionary Tale
Pollard, A. M., Antiquity
Providers and consumers of science
There can be no doubt that isotopic studies have made a huge contribution to archaeology in recent years, so much so that isotope archaeology is now seen as an essential subdiscipline of archaeology in much the same way as isotope geochemistry is a key subdiscipline of geochemistry. Ignoring for current purposes the contribution made by the measurement of a particular radioactive isotope of carbon (14C) since 1950, we can date the beginnings of isotope archaeology to the mid 1960s with the first measurements of lead isotopes in archaeological metals and slags by Brill and Wampler (1965, 1967). This was followed by carbon stable isotopes in human bone collagen in the late 1970s, building on previous work measuring 813C in archaeological bone for radiocarbon determinations (Vogel & Van der Merwe 1977; Van der Merwe & Vogel 1978). Other isotopes followed rapidly, such as nitrogen, oxygen, sulphur and hydrogen for archaeological, palaeoecological or palaeoclimatological purposes and, more recently, the heavier radiogenic isotopes of strontium and neodymium for determining the provenance of organic and inorganic materials (Pollard & Heron 2008).
There is, therefore, nearly 50 years of accumulated experience available on how to use isotopes in archaeology but also, unfortunately, some evidence of how not to use them. The use of lead isotopes in metals as a provenance tool went through a controversial phase in the 1980s and 1990s (Pollard 2009), resulting in nearly a generation during which lead isotopes were almost totally neglected in archaeology: fortunately, this is now changing. There is a danger that the use of the latest fashionable isotope system (strontium in dental enamel) is heading in the same direction, and this paper is written in the hope of preventing this very promising technique suffering the same fate. These dangers are, if anything, more acute now than they were in the 1980s because of the need to demonstrate impact, the measurable effect of a piece of research outside the discipline. Because of the intense public interest in archaeology, it is inevitable that one manifestation of impact is the reporting of research in the media, with the associated hardening of the story whereby the nuances of interpretation are lost in the need to create good stories. The intention of this essay is not to criticise directly any particular piece of work, which would run the danger of taking the debate into the personal arena. It is primarily intended to launch a dialogue between laboratory and field archaeologists about the use of strontium isotopes in archaeology, with the aim of alerting the consumers of such work to what should realistically be expected, and also to remind the producers of the data about the complexity of archaeological interpretation. By suggesting some simple protocols, the aim is to help make sure that such a promising technique does not get lost in hyperbole and subsequent anti-climax.
Having drawn the parallel between isotope archaeology and isotope geochemistry, it is important to appreciate that the use of isotopes in archaeology is different from that in geochemistry. The difference is us: people. People do strange things, but of course it is the study of what people do that makes archaeology so intellectually interesting and at the same time scientifically challenging. This means that the controls on the isotopes we measure in archaeological material are not simply those of biogeochemistry, but are influenced to some degree by human behaviour. As a minimum, this requires that isotope archaeology needs what might be termed an extra interpretative step to account for the contributions of human agency. In fact, because it is in reality much more complicated than that, it might be argued that it demands a completely different approach. The human factors have to be built in to the research design from the beginning.
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